1. Field of the Disclosure
The present disclosure relates to a process for removing phosphorus-containing colloids and their precursors from iron chloride solutions, and more particularly to a process for removing phosphorus-containing colloids and their precursors from iron chloride solutions as filterable products.
2. Background of the Disclosure
In the chloride process for the manufacture of titanium dioxide, acidic metal chloride solutions (containing predominately iron chloride) are formed. These are generally disposed by neutralization, dewatering, and landfill, or deepwelled as hazardous waste after solids removal by settling and/or filtration. In some cases, the solutions are purified and sold as ferrous chloride or ferric chloride solutions, which are used as coagulants in wastewater and potable water treatment. These iron chloride solutions contain chlorides and oxychlorides of titanium, niobium, and zirconium. Macromolecular clusters of titanium, niobium, zirconium or their mixtures with water, chloride, and hydroxide may also form. These clusters typically continue to grow with time, eventually leading to fine precipitates. When phosphorus is also present, it reacts with chlorides and oxychlorides of titanium, niobium, and zirconium or the macromolecular clusters containing these metals to form extremely fine phosphorus-containing colloids. These fine precipitates cause extreme difficulties in solids removal processing of iron chloride solutions by blinding filters, causing slow filtration rates, or interfering with flocculation and settling. These difficulties can lead to titanium dioxide production rate reductions or plant shutdowns. Fine phosphorus-containing precipitates can also cause problems in storage and handling of commercial iron chloride solutions at customers' sites as the precipitates settle and subsequently clog tanks, strainers, and pumping lines. This equipment then needs to be taken out of service for cleaning, incurring costs and interruption of service.
A need thus exists for an improved process for separating impurities such as phosphorus-containing colloids and their precursors from these iron chloride solutions in the form of readily filterable solids.